Transcript Blood Vessels - Learning Central

Clinical Science Team
School of Nursing and Midwifery
Blood vessels
Learning outcomes:
1. Compare the structure of an artery and a vein
2. Explain how the structure of an artery and a vein relates
to its function
3. Describe the structure of a capillary and explain the
physiological significance of this structure
Systemic Circulation
 Arteries.
 Arterioles.
 Capillaries.
 Venules.
 Veins.
 Role is to direct
the flow of blood
from the heart to
the capillaries,
and back to the
heart.
The ARTERY
Arteries carry blood away from the heart.
the elastic fibres allow the
artery to stretch under
pressure
thick muscle and elastic
fibres
the thick muscle can
contract to push the blood
along.
The VEIN
Veins carry blood towards from the heart.
veins have valves which act to
stop the blood from going in the
wrong direction.
thin muscle and
elastic fibres
body muscles surround the veins so that when
they contract to move the body, they also squeeze
the veins and push the blood along the vessel.
Differences in artery and vein
The CAPILLARY
Capillaries link Arteries with Veins
they exchange materials between
the blood and other body cells.
the wall of a capillary
is only one cell thick
The exchange of materials between the
blood and the body can only occur
through capillaries.
The CAPILLARY
A collection of capillaries is known as a capillary bed.
artery
vein
capillaries
body cell
Differences between arteries and veins
Blood Vessels
 Walls composed of 3 “tunics:”
 Tunica externa:

Outer layer comprised of connective tissue.
 Tunica media:

Middle layer composed of smooth muscle.
 Tunica interna:



Innermost simple squamous endothelium.
Basement membrane.
Layer of elastin.
Why do we have different types of blood
vessel?
• Large arteries e.g. aorta are elastic arteries
• Smaller arteries and arterioles are resistance
arteries
• Capillaries can be continuous, fenestrated or
discontinuous, exchange takes place in these
vessels
• Veins are the capacity vessels, approx 64% of
blood is here
Distribution of blood in the vascular system
Blood Vessels & Cardiovascular
system
Monitoring Circulatory Efficiency
 Efficiency of the circulation is
assessed by: pulse and blood
pressure measurements
 Vital signs – pulse and blood
pressure,
respiratory rate and body
temperature
 Pulse – pressure wave caused by
expansion and recoil of elastic
arteries
 Radial pulse (on radial
artery), routinely used
 Varies with health, body
position, activity
Factors Aiding Venous Return
 Venous blood pressure alone is too low to
promote adequate blood return and is
aided by the:
 Respiratory “pump” – pressure
changes created during breathing
suck blood toward the heart by
squeezing local veins
 Muscular “pump” – contraction
of skeletal muscles moves blood
toward heart

Valves prevent backflow during
venous return
Blood flow through the vessels
Blood flow through
vessels is directly
proportional to the
difference in pressure
between the ends
of the tube
Blood flow through the vessels
 Is inversely proportional to the resistance in the vessels.
 Resistance- determined by blood viscosity, vessel length &
vessel radius.
 Blood viscosity & vessel length rarely change, radius can be
changed by vasoconstriction (reducing radius) or
vasodilation (increasing radius)
Blood flow through vessels
 Normally laminar, with the blood components arranged in
layers
 The plasma forms the outer layer & slides smoothly along
the endothelium
 Blood cells form the ‘axial’ layer in the centre of the blood
stream
 This allows the blood to flow smoothly, layers slide over
each other, axial part moves fastest.
Blood flow through vessels
 When we take a blood pressure the sounds we here are
caused by turbulent flow of blood
 Turbulent flow -caused by change in vessel diameter,
increase in velocity, & low blood viscosity
Summary
 Blood vessels carry blood to and from the heart
 Arteries carry blood away from the heart, veins
carry blood back to the heart
 Large arteries are ‘elastic’
 Arterioles provide most of the resistance to blood
flow
 Exchange of nutrients and gases takes place in the
capillaries
 Vein are thin walled and distensible and have
valves to prevent backflow of blood
 Blood circulates through the blood vessels as a
result of pressure changes.